Jack H. Berryman Institute A Landowner’s Guide to Department of Fisheries and Wildlife College of Natural Resources Common North American Predators Utah State University Logan UT 84322-5210 of Upland-nesting Birds For further information please contact the agency listed below. Jack H. Berryman Institute for Wildlife Damage Management, International Association of Fish and Wildlife Agencies, and The Berryman Institute National Fish and Wildlife Foundation The Berryman Institute A Landowner’s Guide to Common North American Predators of Upland-nesting Birds Terry A. Messmer, Michael R. Conover, Raymond D. Dueser, Paul W. Klimack, and Charles E. Dixon 1997 JACK H. BERRYMAN INSTITUTE DEPARTMENT OF FISHERIES AND WILDLIFE COLLEGE OF NATURAL RESOURCES UTAH STATE UNIVERSITY LOGAN, UTAH 84322-5210 1 TABLE OF CONTENTS INTRODUCTION The Prey . 4 The Predators . 6 Predator/Prey Dynamics . 6 Impacts of Predation on Upland-nesting Birds . 7 Breeding Bird Biology, Habitat Use, and Predation . 8 BIOLOGY AND ECOLOGY OF MAMMALIAN PREDATORS Canids Coyote . 9 Red Fox . 10 Domestic and Feral Dogs . 11 Felids Domestic and Feral Cats . 12 Mustelids Badger . 13 Mink . 14 Striped Skunk . 15 Weasels . 16 Procyonids Raccoon . 17 Sciurids Ground Squirrels . 18 THE BIOLOGY AND ECOLOGY OF REPTILIAN PREDATORS Reptilids Lizards . 19 Snakes . 19 Turtles . 20 BIOLOGY AND ECOLOGY OF AVIAN PREDATORS Aves Great-Horned Owl . 20 Red-Tailed Hawk . 21 American Crow . 22 Common Raven . 22 Magpies . 23 SUMMARY . 24 2 This publication provides information designed to increase the reader’s basic understanding of predator/prey interactions and the biology and ecology of com- mon North American predators of upland-nesting birds, their nests, and young. We also discuss the potential impacts of these predators on upland-nesting bird populations. By understanding the biology and ecology of predators, the reader will be better prepared to make informed management decisions about how to enhance local upland-nesting bird populations. Information regarding specific techniques that can be used to manage common predators of upland-nesting birds, can be found in an accompanying publication entitled, “A Landowner’s Guide to Manag- ing Common Predators of North American Upland-nesting Birds.” Most illustrations used in this publication are from “Wildlife Drawings” Copy- right 1980 by the Conservation Commission of the State of Missouri. Used with permission. The badger and long-tailed weasel are line drawings reproductions by Carmen Luna, Jamestown, ND of furbear stamp artwork used in the North Dakota Game and Fish Department’s Furbearer Stamp and Print Program. The original artists are Michael D. Dunn and Van Norby, respectively. The front cover photo was provided courtesy of Alan B. Sargeant, Jamestown, N.D. Funding for this publication was provided by the National Fish and Wildlife Foundation, the International Association of Fish and Wildlife Agencies, the Jack H. Berryman Institute, and a U.S. Fish and Wildlife Service, Division of Federal Aid, Wildlife Restoration Grant. This publication can be cited as: Messmer, T. A., M. R. Conover, R. D. Dueser, P. W. Klimack, and C. E. Dixon. 1997. A landowner’s guide to common North American predators of upland- nesting birds. Berryman Institute Publication No.13, Utah State Univ. Logan. 24 pp. 3 INTRODUCTION The Prey Upland-nesting birds are those bird species that typically nest on the ground (Figure 1). Although most upland-nesting birds nest directly on dry ground, some will nest on floating or standing vegetation located over water. Some upland-nesting birds, such as snow geese (Chen caerulescens), and gulls (Larus spp.) prefer to nest in large colonies on open shore- lines or islands, forsaking concealment for safety in numbers. By nesting in colonies, an individual bird increases the odds that a predator entering the colony will prey on young other than its own. Smaller upland-nesting birds, such as the common nighthawk (Chordeiles minor), prefer to nest on bare ground. The size and coloration of the female, her eggs, and nest afford nesting nighthawks excellent conceal- ment. Other upland- Figure 1 4 Figure 2 nesting birds such as the mallard (Anas platyrhyncos), select nest sites concealed by tall, dense vegetation (Figure 2). Nest site selection is governed primarily by the need to avoid predation. Upland-nesting birds employ other adaptations to increase their chances of raising young. These adapta- tions include anti-predator behavior (e.g., feigning injury), cryptic or camouflage coloration of the females, and the ability to renest if their first nests are destroyed (Figure 3) Figure 3 5 The Predators Evolution has adapted predators to seek prey which provide them with highest returns (in terms of calories and nutrients) for the least expenditure of time and energy. Some preda- tor species employ unique hunting strategies, designed to capture specific prey. Others are opportunistic, taking any prey encountered during the course of daily activities. This publication discusses the ecology of some common North American mammalian and avian predators that can impact avian populations. Other predators not discussed in this publica- tion also will prey on upland-nesting birds, their eggs, and young. Predator/Prey Dynamics When people think of predation, they often visualize a cougar, wolf, or other large carni- vore, killing a deer or elk (Figure 4). In reality, literally thousands of acts of predation (such as a bird eating an insect) occur for each instance of a cougar killing a deer. (Figure 5) Even the large predators kill and eat many more small prey for each large animal taken. The popular belief that predators only kill young, old, sick, and injured animals, thus keeping prey in balance with their habitat, is not entirely true. In natural systems, predator and prey numbers may tend to cycle together. However, few truly natural systems remain. Human activities that alter original habitats have tended to favor some animals at the expense of others. If these activities favor a predator by providing it with alternate food sources or cover during some critical period, predator numbers will increase, and this may result in a greater impact on their prey species. Predators are less abundant than the prey species they pursue. For example, in a given area, the predator community may include one coyote, two great- Figure 4 6 horned owls, and two red-tailed hawks. In this same area, the potential prey base may consist of 100 rabbits, 2,000 birds, and as many as 25,000 mice. In a “balanced” system, when prey num- bers decrease, predator numbers would also be expected to decline. However, problems may arise if predators in- crease in response to abundant alternate food sources. In this situation, preferred populations of prey spcies may be held at unusually low densities by predators. If prey populations are not be able to respond to improved habitat conditions because of predators, the situation is referred to as a “predator pit.” Weather and climate can also affect the physical condition and vulnerability of the prey, thus impact population density, reproduc- tive potentials, and susceptibility to disease. Probably the most important statistic used to Figure 5 determine the impact a predator has on a prey species is the percent of the prey population taken by a specific predator. By knowing this information, managers can implement appropriate strategies to maintain predator and prey species populations in balance with the local habitat conditions. Impacts of Predation on Upland-Nesting Birds Predators can impact upland-nesting bird population in several ways. Adult males and nesting females are preyed upon by a variety of avian (eagles, hawks, owls)(Figure 6), mammalian (coyotes, skunks, raccoons, squirrels), and reptilian (snakes) preda- tors. Predators also eat the young and eggs. However, the actual impact of predation on upland-nesting birds ultimately depends on the composition and density of the predator community, habitat conditions, and the availability of alternate food sources. Figure 6 7 Breeding Bird Biology, Habitat Use, and Predation Upland-nesting bird populations increase under favorable habitat conditions and decrease when conditions deteriorate. Generally upland-nesting birds that select nest sites in narrow strips of cover, such as those found around wetlands in plowed fields and along roads, are less successful due to higher predation rates than those situated in large blocks of continu- ous cover. Upland-nesting bird populations are highest at the end of the reproductive season (late spring or early summer), then decline to yearly lows, which occur just prior to the next reproductive season (Figure 7). Predation may help to moderate population peaks and lows. However, if predator populations are high, upland-nesting bird populations may decline and remain depressed. Current research suggests that in altered habitats, predators can maintain upland-nesting birds at population levels which are lower than what would otherwise occur. For mallards, over-winter female survival of greater than 30% and nest success of greater than 15% may be necessary to maintain local upland-nesting bird breed- ing populations. In areas where female survival and nest success are low, mammalian predators, such as the red fox (Vulpes vulpes), which prey directly on nesting females, can have the greatest impact on bird populations. Figure 7 8 BIOLOGY AND ECOLOGY OF MAMMALIAN PREDATOR CANIDS Coyote ((Canis latrans) Coyotes resemble small “collie” dogs in body form and size (Figure 8). The color of the fur of the upper body is generally gray or reddish-gray with the underparts being a lighter yellowish. A coyote’s coloration may vary by geographic location. Adult coyotes may exceed 50 inches in length and weigh over 50 pounds. Males are larger than females. The body and muzzle are slender, the ears small, pointed, and erect, and the tail is bushy. When running, coyotes carry their tails low. This characteristic helps distinguish them at a distance from domestic dogs and wolves.